This invention relates generally to railroad systems, and more specifically, to methods and system of automatically calibrating track circuits.
A rail track circuit typically is used to detect whether a train is present on a track section. Such circuit also can be used to detect broken rails within the track section and/or can be used to transmit signal aspect information through the rails. A typical track circuit includes rails in electrical series with a signal transmitter and a signal receiver. The signal transmitter applies a voltage, sometimes referred to as a transmit voltage, to the rails. As a result, a current signal, sometimes referred to as a receive current, is transmitted through the rails. The receive current is detected by the receiver.
When a train composed of one or multiple railcars is located on the track section of the track circuit, the wheels of the railcars act as a shunt between the rails and form a shunt path. The shunt path creates an electrical short between the rails at the location of the train, and such short path effectively prevents the receive current from being received/detected by the signal receiver.
Over time, environmental conditions and rail conditions can change. These changing conditions impact ballast resistance of the track circuit. Generally, leakage paths occur through the ballast, and the leakage resistance of such paths varies due to the changing conditions. The varying leakage resistance impacts the receive current. The track circuit therefore is configured, or calibrated, to operate over a range of ballast resistance.
Due to the changing conditions, over time, the track circuit may require re-calibration. Known calibration techniques involve positioning human “maintainers” with two-way radios at the transmitter and receiver. The maintainer at the transmitter communicates data related to the applied voltage to the maintainer at the receiver. The receiver maintainer then informs the transmitter maintainer of the current signal received at the receiver. Adjustments are made to both the transmitter and receiver so that the track circuit operates as desired over the ballast resistance range. Another known calibration technique is for a single human maintainer to perform track circuit calibration by traveling between transmitter and receiver sites (i.e., locations) to make each adjustment. As such, the process of manually calibrating the track circuit settings may be costly, inefficient, and/or time-consuming.